Process for the manufacture of artificial crystals



March 18, 1952 M. TOURNIER ,58 ;3

PROCESS FOR THE MANUFACTURE OF ARTIFICIAL CRYSTALS Filed Feb. 12, 1948 INVENTOR ATTO R N EY MARCE L TOURN/ER Patented Mar. 18, 1952 PROCESS "FOR THE MANUFACTURE OF ARTIFICIAL CRYSTALS Marcel Tournier, Paris, France, assignor to International Standard Electricflorporation, N ew York, N. Y., a corporation of Delaware Application February 12, 1948,;'S.erial No. 7,878 :In France ctober25, 1946 Section LilublicLaw 691), August 8,1946 Patent expires October 25,1966

16 Claims. (0133-4501) The present invention relates tothepreparation of artificial crystals, such as "piezoelectric crystals, from a supersaturated solution of the salt of the crystaldesired.

When crystals are caused to crystallise in a solution which is supersaturated, great difiiculty is encountered due to the presence in the solution of dust and suspended particles. Such particles form centres of crystallisation on whichare deposited microscopic crystals. The majority of these fall to the bottom of the receptacle quite slowly and rob the solution of strength, in such a way that the large crystalsthat one desires to obtain are seldom obtained. Furthermore some of the microcrystalline particles "in suspension in the solution become fixed on the surfaces of the large crystals in positions that do not correspond to the general disposition of ions in the principal crystalline lattice. This results in local flaws which cause inclusions of supersaturated solution in the crystal.

It is known that the seriousness of these factors can be reduced by various procedures, such as filtering, centrifugin etc. These methods diminish the number of dangerous parasitic particles but do'not remove them entirely.

An object of the present invention is to provide means for obtaining supersaturated solutions for the preparation of artificial crystals not containing impurities. A further object is to provide means whereby parasitic crystal nuclei which may form in the solution during the growth of the desired crystals maybe prevented from adhering to the desired crystal and interfering with its regular growth.

According to one feature of the invention-the supersaturated solution .is submitted to amplitude vibrations of frequencies such that the parasitic crystals described above are produced very rapidly; then the solution is freed from the crystals thus formed. For this purpose it may be desirable to employ ultrasonic frequencies.

According to another feature of the invention, the solution is stirred during the application of the ultrasonic waves, in order to ensure that the parasitic particles pass through the ultrasonic beam.

A description of a process employing the principles of this invention is given below which should be read in conjunction with the accompanying drawings, in which:

Figure 1 is a vertical section of an apparatus employing the principles of this invention;

Figure 2 is a schematic section of an apparatus taken through the plane A-B of Figure 1.

In a container I, preferably transparent, maintained at any desired temperature by a regulated heating system (not shown) a saturated solution of a salt is prepared at a given temperature. To

simplify the description, we will suppose that it isdesiredto obtain piezoelectric crystals of monphosphate of ammonia; it Will be quite evident 'that the procedure is as well applied to crystals of other salts, providing the appropriate temperatures and concentrations are employed. In litresof water heated for example, to a temperature of 50 C., are dissolved69.5 kg. of monphosphate of ammonia; there is thus obtained a saturated solution at 50; the mixture is stirred,

these crystals forming on the particles in suspension. These particles are then, therefore, rapidly encased in small crystals which cause them to become heavy and to fall to the bottom of the receptacle. Owing to the operation of propeller 2, the solution is made to pass through the ultrasonic beam.

When the density of the solution in this example has become that of a solution saturated at 45C., the production of the ultrasonic waves, .and'the operation of propeller 2 are stoppedallowing the crystals to fall to the bottom of the receptacle, which has preferably a bottom 4 of conical form, supplied with a-tube5 and a stopcock 6. Care has been taken to apply to the surface of the solution before the action of the ultrasonic beam a film l of a neutral liquid, such as oil of Vaseline which prevents the introduction of dust particles into the solution.

The crystals which are deposited at the bottom of container 1, are siphoned off by means of stopcock 6, and it is verified'by causing a luminous beam to travel through the solution that the solution is optically transparent.

After having eliminated all the crystals and all their germs, which have been combined with the dust particles in the suspension of the solution, the solution is re-heated several degrees to redissolve any nuclei which remain in the container; then is allowed to cool to 40 C. for example, which furnishes a supersaturated solution which is free from impurities. There are then plunged into the solution one or more crystalline nuclei which it is desired to cause to increase, suspended for example by means of supports 9, continuing to stir the solution by means of propeller 2, until the nuclei have grown into crystals of the desired dimension.

Other crystalline particles can accidentally reform in the solution, and may be deposited on the crystal under formation. The suspension of these undesirable nuclei can be avoided by disposing, for example, along the vertical walls of container I, plates II] which may be vertical. Because of the stirring efiect of the propeller 2, these nuclei arrive in contact with the said plates where they are stopped and then fall to the bottom of the container. At the bottom of these plates may be placed small funnels ll, provided with evacuation tubes [2 closed by stopcocks l3, in order to evacuate these undesired particles from the solution. Equally heating elements [4 may be provided in the funnel l l, which elements may be, for example, electrical resistances, which locally elevate the temperature of the solution, and create a redissolution of the crystals thus deposited. This last device also avoids useless loss of the strength of the solution and permits one to obtain larger crystals in a given volume of solution under given temperature conditions.

Although the invention has been described with respect to one particular embodiment and for a particular kind of crystal, it is clear that it is not limited to this example, and that there may be many other forms of apparatus and elements employing the principles of the present invention, and that these may be applied to crystals of a different nature without departing from the spirit of the invention.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1'. A process for preparation of artificial crystals comprising the steps of obtaining a supersaturated solution of a salt in a solvent, applying to said supersaturated solution mechanical vibrations, eliminating any deposit of crystal nuclei formed on impurities in said solution by said mechanical vibrations, then introducing into said solution crystal nuclei to constitute the centers of the desired crystals, and forming said crystals on said nuclei.

2. A process for the preparation of artificial crystals such as piezo-electric crystals, by crystallization from a supersaturated solution, comprising the dissolving of a salt in a solvent at a predetermined temperature, the protection of the surface of the resulting solution by a neutral liquid with which it is non-miscible, mechanical stirring of said solution, a cooling of the solution produced to obtain a supersaturated solution, the application to the said supersaturated solution of mechanical vibrations to rapidly form crystalline nuclei on impurities present in said solution, the elimination from said solution of said parasitic crystalline nuclei, and the introduction into the said solution of one or more crystalline nuclei to constitute the centers of the desired crystals, whereby the desired crystals may be grown in said supersaturated solution substantially free from the interference of parasitic crystalline nuclei.

3. The process according to claim 2, and further comprising the steps of re-heating said solution to dissolve any parasitic crystalline nuclei which accidentally remain in suspension after said solution is subjected to said mechanical vibrations and re-cooling said solution to again obtain a supersaturated solution.

4. A process according to claim 2, comprising local heating to redissolve any parasitic crystal nuclei produced throughout the said supersaturated solution during the growth of the crystal or crystals which it is desired to obtain.

5. The process according to claim 2 in which said mechanical vibrations are of ultrasonic frequencies.

6. The process according to claim 2, and further comprising the elimination of newly formed parasitic crystalline nuclei from said supersaturated solution during the growth of the desired crystals, by the continuous agitation of said solution to force said parasitic nuclei to suitable evacuation points.

MARCEL TOURNIER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 19,697 Kjellgren Sept. 10, 1935 1,835,271 Burke et a1. Dec. 8, 1931 1,841,040 Lindberg Jan. 12, 1932 1,845,742 Cocksedge Feb. 16, 1932 1,922,283 Dering Aug. 15, 1933 FOREIGN PATENTS Number Country Date 352,419 Great Britain July 7, 1931 477,646 Great Britain Jan. 4, 1938 OTHER REFERENCES Chambers et al., The Use of Microcrystans of Sulfathiazole in Surgery, Journal American Medical Association, May 23, 1942, pages 324-7. 

1. A PROCESS FOR PREPARATION OF ARTIFICIAL CRYSTALS COMPRISING THE STEPS OF OBTAINING A SUPERSATURATED SOLUTION OF A SALT IN A SOLVENT, APPLYING TO SAID SUPERSATURATED SOLUTION MECHANICAL VIBRATIONS, ELIMINATING ANY DEPOSIT OF CRYSTAL NUCLEI FORMED ON IMPURITIES IN SAID SOLUTION BY SAIDSAID MECHANICAL VIBRATIONS, THEN INTRODUCING INTO SAID SOLUTION CRYSTAL NUCLEI TO CONSITUTED THE CENTERS OF THE DESIRED CRYSTALS, AND FORMING SAID CRYSTALS ON SAID NUCLEI. 